- What is Abdominal Aortic Aneurysm ?
- How to Diagnosis?
- What is the management of abdominal aortic aneurysm?
- Endovascular management?
Abdominal Aortic Aneurysm (AAA) are the most common type of arterial aneurysm, occurring in 3% to 10% of people older than 50 years of age in the Western world (Br J Surg 1998;85:155). They are five times more common in men than in women and 3.5 times more common in whites than in African Americans.
. Ninety-five percent of Abdominal Aortic Aneurysmss are infrarenal, 25% involve the iliac arteries, and 2% involve the renal or other visceral arteries (J Cardiovasc Surg 1991;32:636). Four percent are associated with peripheral (e.g., femoral or popliteal) aneurysms.
- Clinical manifestations. Seventy-five percent of Abdominal Aortic Aneurysmss are asymptomatic and are found incidentally. Aneurysm expansion or rupture may cause severe back, flank, or abdominal pain and varying degrees of shock. Distal embolization, thrombosis, and duodenal or ureteral compression can produce symptoms. Fifty percent of Abdominal Aortic Aneurysmss are identifiable on physical examination as a pulsatile mass at or above the umbilicus. The differential diagnosis includes a tortuous aorta or an abdominal mass lying adjacent to the normal aorta that might transmit aortic pulsations (e.g., lymphoma, pancreatic pseudocysts or carcinoma, mesenteric masses). Abdominal Aortic Aneurysms rupture may mimic renal colic, peritonitis, duodenal perforation, pancreatitis, degenerative spine disease, acute disk herniation, or myocardial infarction.
- Abdominal cross-table lateral films. In 75% of patients with an Abdominal Aortic Aneurysms, arterial wall calcification suggests the presence of an aneurysm and permits a gross estimation of aneurysm diameter.. The 5-year risk of rupture is plotted against aneurysm size, showing the sharp increase in risk of rupture beyond a diameter of 6 cm.
- Ultrasonography and computed tomography (CT) scanning demonstrate Abdominal Aortic Aneurysmss with an accuracy of 95% and 100%, respectively, and are useful for serial examinations of small aneurysms. CT angiography is rapidly becoming the gold standard for evaluating Abdominal Aortic Aneurysmss because it allows operative planning for endovascular approaches.
- Magnetic resonance (MR) scan is comparable to CT but avoids radiation exposure and is useful in patients with intravenous contrast contraindications.
- Aortography is not sensitive for the diagnosis of Abdominal Aortic Aneurysms because it may underestimate the aneurysm size or fail to reveal the aneurysm owing to the presence of mural thrombus. However, aortography is indicated to evaluate suspected renal or mesenteric artery stenosis and lower-extremity occlusive disease .
C.Elective management of abdominal aortic aneurysm
- The risk of aneurysm rupture correlates best with aneurysm size . However, even small aneurysms can rupture.
- Medical management. Patients with small aneurysms (<4.5 cm in diameter) without risk factors for rupture can be followed using ultrasound or CT scan yearly, and patients with larger ones are followed more frequently. Smoking cessation, control of hypertension, and treatment of chronic pulmonary obstructive disease are very important Doxycycline is being investigated as an agent that may retard aneurysm growth, based on its MMP-inhibiting properties (J Vasc Surg 2001;34:606).
- Elective surgical treatment. Operative mortality ranges from less than 5% for uncomplicated Abdominal Aortic Aneurysms to greater than 50% for ruptured Abdominal Aortic Aneurysms (Br J Surg 1998;85:1624). Five-year survival after elective repair of Abdominal Aortic Aneurysms is no different from that for age-matched patients without Abdominal Aortic Aneurysms. Associated cardiovascular disease, hypertension, decreased renal function, chronic obstructive lung disease, and morbid obesity increase operative risk (Arch Intern Med 1995;155:1998). Table 18-1 outlines the cardiac evaluation of patients with an Abdominal Aortic Aneurysms. Indications for surgical management for Abdominal Aortic Aneurysmss include the following:
- Symptomatic aneurysms of any size.
- Aneurysms exceeding 5 cm diameter.
- Increase in diameter by more than 0.5 cm/year
- Saccular aneurysms (due to potential for active infection).
- Relative indications for repair of smaller Abdominal Aortic Aneurysmss include poorly controlled hypertension (diastolic blood pressure ≥100 mm Hg) and significant chronic obstructive pulmonary disease (1-second forced expiratory volume <50% of predicted value) (Ann Surg 1999;230:289).
- to elective repair include recent myocardial infarction, intractable congestive heart failure, unreconstructible coronary artery disease, life expectancy of less than 2 years, and incapacitating neurologic deficits after a stroke.
In the standard repair, the aneurysm is approached through a midline abdominal incision and exposed by incising the retroperitoneum. Alternatively, a left retroperitoneal approach is advantageous in obese patients, those with chronic pulmonary obstructive disease, and patients with previous intraabdominal surgery. In addition, proximal control of the aorta at the mesenteric level or above is more easily achieved via this approach. Next, the duodenum and left renal vein are dissected off the aorta in the transabdominal approach. After heparinization, the aorta and iliac arteries are cross-clamped. Aortotomy is then made and extended longitudinally to the aneurysm “neck,” where the aorta is either transected or cut in a T fashion. The aneurysm is opened, thrombus is removed, and bleeding lumbar arteries are suture ligated. The proximal anastomosis is performed to nonaneurysmal aorta using a tube or bifurcation graft. The distal anastomosis is completed at the aortic bifurcation (tube graft) or at the iliac or femoral arteries (bifurcation graft), as the disease dictates. After the clamps have been removed and hemostasis is ensured, the aneurysm wall is closed over the graft.
F. Endovascular management
- Endovascular management of Abdominal Aortic Aneurysmss has dramatically decreased the acute morbidity of open surgery. It is important to note that the indications for endovascular treatment of Abdominal Aortic Aneurysms are no different than those for traditional open operative repair.
- The most important selection criterion for endovascular treatment of an Abdominal Aortic Aneurysms is aortoiliac anatomy. Assessment of the Abdominal Aortic Aneurysms on preoperative CT angiogram includes the following factors:
- Length and diameter of nondilated and healthy infrarenal aorta (the neck). Most devices require a proximal neck that is 1.5 cm long, and some devices allow suprarenal attachment with an open stent segment. Current endograft dimensions at the proximal end are up to 36 mm in diameter.
- Angle between the neck and aneurysm. Significant angulation between the neck and adjacent aneurysm (>45 degrees) makes proximal graft deployment technically difficult and is associated with a higher risk of treatment failure.
- Presence of intraluminal thrombus. Significant mural thrombus or atheroma in the proximal neck can prevent adequate sealing of an endograft and therefore represents a relative contraindication for endovascular treatment.
- Shape of the aortic neck. The proximal neck segment geometry is also important in that a cone-shaped neck or reverse taper (i.e., widens more distally) precludes adequate apposition of the endograft to the aortic wall.
- All currently approved endovascular grafts are bifurcated and extend to the iliac arteries. Iliac artery tortuosity, calcification, and luminal narrowing, in combination with the profile of the delivery system, are critical for successful endograft delivery and deployment without complication.
- Patent aortic branches may influence the decision as to whether to proceed with endograft placement. A renal artery or large accessory renal artery arising from the proximal neck or the presence of a horseshoe kidney with multiple renal arteries is often a contraindication for endograft placement. Patent lumbar arteries arising from the aneurysm do not preclude endograft placement. A patent inferior mesenteric artery (IMA) associated with large mesenteric collaterals (e.g., meandering mesenteric artery) or a large patent IMA suggests abnormal mesenteric blood supply and risk of large-bowel ischemia with endograft coverage of the IMA orifice. Therefore, these vascular patterns are contraindications to endograft placement.
Complications of endograft repairs of Abdominal Aortic Aneurysmss
- Early complications include branch occlusion, distal embolization, graft thrombosis, and arterial injury (especially external iliac artery avulsion at the common iliac bifurcation in patients with small, calcified, diseased iliac arteries). These complications are often corrected endovascularly but may require emergent conversion to open repair.
- Arterial dissection may occur with device introduction, but this may not require additional treatment if the endograft spans the segment of dissection. Additional stents can be used to treat the dissected vessel if necessary.
- As with open surgical Abdominal Aortic Aneurysms repair, bowel ischemia may occur postoperatively secondary to embolization or hypoperfusion, but it is rare. Renal dysfunction may occur because of the nephrotoxicity of the contrast agent used for intraoperative angiography or because of direct injury due to embolization or renal artery occlusion.
- Graft migration occurs in 1% to 6% of patients, is associated with challenging arterial anatomy and poor graft placement, and can typically be treated with secondary endovascular procedures.
- Endoleak is defined as failure to exclude the aneurysmal sac fully from arterial blood flow, potentially predisposing to rupture of the aneurysm sac (J Endovasc Surg 1997;4:152). Management strategies for endoleaks discovered on follow-up imaging studies are evolving. For any endoleak that is associated with aneurysm sac enlargement, intervention is required. Endoleaks are usually corrected by endovascular means but may require conversion to open surgical repair.
- In general, endoleaks from the proximal or distal attachment sites (type I) warrant intervention because these are frequently associated with increasing aneurysm sac size. Proximal endoleaks may be sealed with angioplasty, placement of a stent, or an endovascular graft component.
- Type II endoleaks are due to collateral flow (IMA, lumbar arteries) and are generally closely observed. Type II endoleaks may be treated with embolization through collateral vessels (via the hypogastric artery for lumbar branch bleeding, via the superior mesenteric artery for IMA bleeding) or directly through the aneurysm sac via a translumbar approach, which is usually the most successful strategy.
- Type III endoleaks are usually due to component separation, and they should be corrected as soon as they are diagnosed.
- Type IV endoleaks are due to porosity of the graft material and are usually self-limiting.
- Relative to open surgical repair, endovascular treatment of Abdominal Aortic Aneurysms is associated with a reduction in perioperative morbidity, shorter duration of hospitalization (J Vasc Surg 2003;37:262), and reduction of perioperative mortality (J Vasc Surg 2000;31:134). The short- and mid-term results are encouraging and are similar to results seen with open repair, but long-term results are not yet available. Close follow-up with CT scanning every 6 months initially and yearly after the first year is essential to understand the behavior of these devices. Future fenestrated and branched devices may allow treatment of pararenal and other more complex Abdominal Aortic Aneurysmss.